linux-kernel - [PATCH v2 1/3] pm: at91: pm_suspend: add the WFI support for ARMv7

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Message-ID: <1422411757-13066-1-git-send-email-wenyou.yang@atmel.com>
Date:	Wed, 28 Jan 2015 10:22:37 +0800
From:	Wenyou Yang <wenyou.yang@...el.com>
To:	<nicolas.ferre@...el.com>, <linux@....linux.org.uk>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>,
	<alexandre.belloni@...e-electrons.com>,
	<sylvain.rochet@...secur.com>, <peda@...ntia.se>,
	<sergei.shtylyov@...entembedded.com>, <linux@...im.org.za>,
	<wenyou.yang@...el.com>
Subject: [PATCH v2 1/3] pm: at91: pm_suspend: add the WFI support for ARMv7

Add the WFI support to put the cpu to the sleep state.

In the meanwhile, disable the processor's clock.

Signed-off-by: Wenyou Yang <wenyou.yang@...el.com>
---
 arch/arm/mach-at91/pm_suspend.S |   49 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-at91/pm_suspend.S b/arch/arm/mach-at91/pm_suspend.S
index 122a3f1..aed6903 100644
--- a/arch/arm/mach-at91/pm_suspend.S
+++ b/arch/arm/mach-at91/pm_suspend.S
@@ -53,6 +53,53 @@ mode	.req	r6
 	beq	1b
 	.endm
 
+/*
+ * Put the processor to enter the WFI state
+ */
+	.macro _do_wfi
+
+#if defined(CONFIG_CPU_V7)
+	/*
+	 * Execute an ISB instruction to flush the pipeline to ensure
+	 * that all of operations have beem completed.
+	 */
+	isb
+
+	dsb
+	dmb
+
+	/* Disable the processor's clock */
+	mov	tmp1, #AT91_PMC_PCK
+	str	tmp1, [pmc, #AT91_PMC_SCDR]
+
+	wfi
+
+	/*
+	 * CPU can speculatively prefetch the instructions
+	 * so add NOPs after WFI. Sixteen NOPs as Cortex-A5 pipeline.
+	 */
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+#else
+	mcr	p15, 0, tmp1, c7, c0, 4
+#endif
+
+	.endm
+
 	.text
 
 /*
@@ -181,7 +228,7 @@ sdr_sr_done:
 
 skip_disable_main_clock:
 	/* Wait for interrupt */
-	mcr	p15, 0, tmp1, c7, c0, 4
+	_do_wfi
 
 	tst	mode, #AT91_PM_SLOW_CLOCK
 	beq	skip_enable_main_clock
-- 
1.7.9.5

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